Supporters and family members of Berta Cáceres, the Honduran environmental and indigenous rights activist who was assassinated last year, have confronted the country’s president in Washington to demand an independent investigation of her murder.

President Juan Orlando Hernández traveled to Washington to meet with lawmakers on Tuesday and was greeted by protesters carrying signs with photographs of murdered activists and chants of “asesino” – Spanish for murderer.

Cáceres was one of more than 120 land and environmental campaigners murdered since a military-backed coup d’état ousted the democratically elected president Manuel Zelaya in 2009, according to the anti-corruption NGO Global Witness. Eight men have been arrested in connection with her murder, including one serving and two retired military officers.

Human rights organizations have joined the family in calling for an international independent investigation into her death.

“We want to have an independent investigation to follow up on what the justice in Honduras has done so far,” said Neery Carrillo, Cáceres’s sister. “We don’t trust the justice in Honduras.”

The Honduran government has denied any role in Cáceres’s killing, but records obtained by the Guardian show that one of the suspects had been appointed chief of intelligence for elite special forces and that he and another suspect received military training in the US.

During the meeting, Mark Pocan, a Democratic congressman from Wisconsin, raised concerns that some of the suspects in the murder had received US training, according to an aide in the congressman’s office. The congressman asked the president how to ensure that US aid money was not being used to abet human rights violations.

Pocan, who met with Cáceres’s sister and niece before the meeting with the president, said he raised their demand for an independent inquiry into her murder.

Hernández argued that his government was making strides in combating the violence that has devastated this country, one of the most deadly in the world, and said local authorities had done an adequate job investigating her death, according to Pocan’s office.

Cáceres led the decade-long struggle against a project to build a dam along the Gualcarque River, on territory that is sacred to the Lenca people and could flood large areas of ancestral lands and cut off water supplies to hundreds.

She was murdered late in the evening on 2 March 2016, after at least four gunmen stormed her home in a gated community on the outskirts of a town called La Esperanza.

The murder of Cáceres, recipient of the prestigious Goldman Environmental prize in 2015, sparked international outcry and calls for US to suspend aid to the country. The Honduran government, which receives tens of millions of dollars in annual US aid, is under mounting pressure to conduct an independent inquiry into the crime.

Her family is supporting the Berta Cáceres Human Rights in Honduras Act, a bill that would suspend US funding for security assistance until basic human rights conditions are met. The legislation was reintroduced by Hank Johnson, a Democratic congressman from Georgia, on the one-year anniversary of Cáceres’ death.

Silvio Carrillo, her nephew, a US citizen who lives in Oakland, California, said the government was “absolutely implicated” in his aunt’s death.

“They’ve got eight guys in custody there but these aren’t the intellectual authors,” Carrillo said.

“There is a direct tie – straight up, way high up into the army and into the government, but I think there’s a fear of finding out too much.”

Last year, a former Honduran soldier told the Guardian that he had seen Cáceres’s name on a hit list that was passed to US-trained units by the Honduran military joint chiefs of staff.

The soldier said that two elite units had been given lists featuring the names and photographs of activists – and ordered to eliminate each target. Honduran authorities have denied the allegations.

The protesters waited outside of a meeting room in the Cannon building. As Hernández left, Cáceres’ niece shouted a question about the investigation but the president, swarmed by security, did not turn his head.